We propose to continue our work on the function of the human erythrocyte membrane proteins in endocytosis and disease states by performing the following studies: attempts will be made to identify the sites where calcium associates with the membrane by using fractions of membranes (inside-out vesicles, Triton shells) and purified membrane components both alone or reassembled so as to mimic the components as they exist at the cytosol face of the RBC membrane; the site of localization of the drugs that induce RBC endocytosis will be detected by using 3H-chloropromazine and 3H-vinblastine and measuring their binding to fractions of membranes and isolated membrane components alone or reassembled to mimic various areas of the membrane; the redistribution of spectrin and actin within the cytoskeleton will be studied by using a polyclonal anti-spectrin and a monoclonal antispectrin band 2 both labelled with the immunoferritin technique, and biotinylated heavy meromyosin to which immunoferritin tagged avidin will be bound to identify membrane actin. The distribution of membrane cytoskeletal proteins will be followed during white ghost endocytosis in erythrocytes derived from normal controls and from patients with a variety of erythrocytic disorders; a possible RBC myosin - the actin-activated ATPase - will be measured in RBC from patients with erythrocytic disorders to determine if the disorder affects a putative contractile protein.